A report by Dr. John Howard, di rector of the National Institute for Occupational Safety and Health, concluded there is insufficient evidence linking post-9/11 work at Ground Zero to cancer.

Cancer, he says, is far too common to be able to link specific cases to work at the rubble. Indeed, said Howard, “drawing causal inferences . . . in responders and survivors is especially challenging.”

Not surprisingly, his conclusion has drawn the ire of responders and their families, as well as the usual gaggle of local pols.

But it supports those who have argued for years that it’s wrong to presume that all illnesses later suffered by those who worked at Ground Zero were caused by that effort — and that treatment thus should be subsidized by the taxpayers.

Let’s be clear: Every single hero sickened by 9/11 toxins deserves absolute, unstinting care at public expense.

But automatically presuming, without proof, that illnesses were caused by Ground Zero work is not justifiable.

Howard’s study was mandated by the so-called Zadroga Act, which authorized $4.3 billion to monitor and treat those sickened by Ground Zero exposure.

Opportunists moved in.

The law itself is named for James Zadroga, an NYPD detective whose death some linked to rescue work at Ground Zero — even though the New York City medical examiner found “beyond certainty of doubt” that it was caused by injected, ground-up prescription drugs. No trace of Ground Zero particles was found in Zadroga’s lungs.

Then there was NYPD Officer Cesar Borja, another Zadroga Act icon, who died after reportedly working “16-hour shifts” at Ground Zero. In fact, he’d directed traffic for a few days — away from the site, weeks after the attack.

Tort lawyers were angling for a Ground Zero payday from Day One. At one point, they’d cited “387 different diseases or conditions, all attributable to 9/11 exposure” — including illnesses that couldn’t possibly be Ground Zero-related.

As for the scientists at Mount Sinai Hospital who’ve been tracking those illnesses, The New York Times reported that their findings have been derided by experts as “scientifically questionable” and as “exaggerating the health effect with imprecise descriptions of workers’ symptoms.”

Under the Zadroga Act, however, there will be periodic reviews of Howard’s findings, starting as early as next year — so he may well reverse himself.

If the science supports that, fine.

But if such a decision is driven by emotion, politics and greedy tort lawyers — well, not so fine.